Download DRAKE R-4A Specifications
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TABLE OF CONTENTS General Specifications 3 I General Description 5 II Installation Instructions 6 A. B. C. D. E. F. G. Unpacking Location Power Requirements Antenna Requirements Speaker Requirements Anti-VOX Muting III Control Functions A. B. c . 9 Front Rear Jacks Side Controls & Jacks IV Operation Preliminary Control Settings B. Single Sideband or Double Sideband Suppressed Carrier Reception c. C. W. Reception D . AM Reception E. RTTY Reception F . Adjusting Dial Calibration G . Noise Blanker Operation H. Operation of Notch Control I . Accessory Frequency Coverage J. Fixed Frequency Operation V Theory of Operation J. K. 9 11 12 13 A. A* B. c . D. E. F. G. H. I. 6 6 6 6 7 7 7 13 13 13 14 14 15 15 16 17 20 21 R. F. Amplifier First Mixer and Premixer System Second Converter 50 KC I. F. System Detector Systems Audio Output AVC System S Meter Noise Blanker Crystal Calibrator Power Supply -l- 21 21 22 22 22 24 24 24 25 25 25 27 VI Service Data A, B. C. D. Removing Top Cover Removing Bottom Cover Tube Replacement Troubleshooting 32 VII Alignment Instructions A. B. c . D. E. F. G. H. I. J. 27 27 27 27 50KC Oscillator Alignment 50KC I. F. Alignment Crystal Filter and Filter Match Transformer Alignment 5595 KC Oscillator Alignment Antenna RF, and Injection Circuit Alignment 100 KC Calibrator Alignment V.F.O. Adjustment Notch Filter Alignment Passband Tuner Alignment Bias and S-meter adjustment 32 32 33 33 34 35 35 35 35 36 CHARTS AND ILLUSTRATIONS Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig., Fig. # # # # # # # # # # # # # 1 2 3 4 5 6 7 8 9 10 11 12 13 Connecting R-4A to TR-4 Transceiver Viewing Angle Option Rear View Crystal Freg. Chart Pre selector Chart Selectivity C urve s Notch Curves Block Dia gram Voltage Chart Resistance Chart Top View Bottom View Schematic Diagram -2- 8 8 12 18 19 23 23 26 28 29 30 31 37 GENERAL SPECIFICATIONS FREQUENCY COVERAGE: 3 . 5 - 4 . 0 MC , 7.0-7.5Mc, 1 4 . 0 - 1 4 . 5 , 21.0-21.5, and 28.5-29.0 MC with crystals supplied. Ten accessory crystal sockets are provided for coverage of any 10 additional 500 KC ranges between 1.5 and 30 MC with the exception of 5.0-6.0 M C . SELECTIVITY: Drake tunable passband filter provides: .4 KC at 6 DB down and 2.6 KC at 60 DB 1.2 KC at 6 DB down and 4.8 KC at 60 DB 2.4 KC at 6 DB down and 8.2 KC at 60 DB 4.8 KC at 6 DB down and 20 KC at 60 DB Selectivity switching is independent of detector and AVC down down down down switching. I. F . FREQUENCIES: First I. F. - 5645 KC crystal lattice filter; second I.F. 50 KC tunable L/C filter. STABILITY: Less than 100 cycles after warm up. line voltage change. Less than 100 cycles for 10% SENSITIVITY: Less than .5 uv for 10 DB signal plus noise to noise on all amateur bands. MODES OF OPERATION: SSB, CW, AM, RTTY DIAL CALIBRATION: Main dial calibrated 0 to 500 KC and 500 to 1000 KC in 5 KC divisions. Vernier dial calibrated 0 to 25 KC in 1 KC divisions. CALIBRATION ACCURACY: Better than 1 KC when calibrated at nearest 100 KC point. AVC: Amplified delayed AVC having slow (. 75 sec .) or fast (. 025 sec.) discharge; less than 100 microsecond charge. AVC can also be switched off. 3 DB change in AF output with 60 DB change in RF input. AUDIO OUTPUT: 1.4 watts max. and .5 watts at AVC threshold. AUDIO OUTPUT IMP EDANCE: 4 ohms and hi impedance for anti-vox. ANTENNA INPUT: Nominal 52 ohms. SPURIOUS RESPONSES: Image rejection more than 60 DB. I. F. rejection more than 60 DB on ham ranges. Internal spurious responses in ham ranges less than the equivalent 1 uv signal on the antenna. -3- TUBES AND SEMICONDUCTORS: TUBE FUNCTION 12BZ6 12BA6 6HS6 6HS6 12BE6 12BA6 12BA6 2N3394 2 - 2N3394 6EH5 12BA6 12AX 7A 2N706 2N3858 2N3394 lN714 0B2 and lN483A 2 - lN3194 lN3194 lN270 and 2N3394 2 - lN483A lN483A lN483A 2 - lN270 R.F. amp. 100 KC calibrator 1st mixer Premixer 2nd mixer and xtal oscillator 50 KC I.F. 50 KC I.F. AVC amp./AVC det. Audio amp. Audio output Noise blanker amp. Noise blanker amp. /shaper VFO VFO buffer Xtal oscillator Voltage regulator Voltage regulator Power supply rectifiers Bias rectifier AM detector Noise blanker pulse clippers Noise blanker gate Switching Prod. det. FRONT PANEL CONTROLS: Main tuning, AF gain, RF gain, SSB/CW-AM with slow AVC, fast AVC, or AVC off, function switch, band switch,xtal switch, passband tuning and selectivity, preselector, notch, and headphone jack. REAR AND SIDE JACKS AND CONTROLS: S-meter zero, notch adjust, antenna jack, speaker jack, mute jack, anti-vox jack, T4/T4X injection jack, accessory power socket, crystal lock socket, xtal/VFO switch, ground post , and fuse post. POWER CONSUMPTION: 60 watts, 120/240 VAC, 50/60 cycles. DIMENSIONS: 5-l/2” high, l0-3/4” wide, cabinet depth ll-5/8”, overall length 12-l/4”, weight 16 lbs. -4- I GENERAL DESCRIPTION The DRAKE R-4A is an extremely versatile communication receiver designed to bring you every feature desirable for the ultimate in the reception of all modes of amateur communications. It provides a linear permeability-tuned solid state VFO with 1 KC readability, and premixed injection with crystal controlled high frequency oscillator for stability on all bands. A 100 KC crystal calibrator is built-in. An improved passband tuner/filter with four selectivity positions, and a built-in notch filter are incorporated to provide the desired selectivity and interference rejection, and a noise blanker is built-in for elimination of most noise on CW, SSB and AM. As supplied, the unit gives complete coverage of 80, 40, 20, and 15 meter bands as well as the 28.5 MC to 29 .O MC portion of 10 meters. Ten accessory crystal sockets are provided for coverage of other 500 KC frequency ranges between 1.5 and 30 MC such as 160 Meters, MARS frequencies, WWV, short wave broadcast, etc. These sockets can be programed to give up to 5 MC of continuous coverage for convenient use with V. H. F. converters. The R-4A also includes time proven DRAKE AVC with fast-attack/slowrelease for SSB or AM and fast-attach fast-release for CW. If desired, the AVC can be completely disabled for CW reception. Complete AVC action and accurate S-meter indication can be obtained, on all modes. A crystal-lattice filter following the first mixer provides excellent overload characteristics by providing selectivity before gain producing stages. When used with our T-4 Reciter, transceive operation may be obtained, and when used with the T-4X transmitter, either transceive or independent receive and transmit functions are possible. -5- II INSTALLATION INSTRUCTIONS A. UNPACKING Carefully remove your R-4A from the packing carton and examine it closely for signs of shipping damage. Should any be apparent, notify the delivering carrier immediately, stating the full extent of the damage. Fill out and mail the enclosed warranty registration card so that your warranty will be effective. Save the packing material. You may need it later for reshipment or storage. Inspect the packing material closely before putting it away to be sure that you have not overlooked any accessory hardware. B. LOCATION In general the location of the R-4A is not critical. However, care should be taken to insure that space is allowed around the unit for adequate air circulation. Extremely hot locations, such as near radiators or heating units, should be avoided. Do not cover the top of the R-4A with books, papers, or pieces of equipment, as overheating may result. c. POWER REQUIREMENTS The R-4A is supplied with a dual-primary power transformer and can be operated from 120 or 240 volt 5 0 / 6 0 cycle AC. As supplied from the factory, it is wired for 120 volt operation. If 240 volt operation is desired, it will be necessary to remove the black/yellow and black/green power transformer primary wires from the terminals to which they are now connected and connect them together at the unused terminal on the same terminal strip. It will also be necessary to replace the . 75 amp fuse supplied with the unit with a .4 amp Slo-Blo fuse for adequate protection at the increased voltage (see schematic diagram). D. ANTENNA REQUIREMENTS The R-4A is designed to give best results when used with an antenna resonant on the operating frequency and having an impedance from 50 to 75 ohms. This requirement is most easily met using a center-fed dipole antenna cut to the desired frequency and fed with RG58A/U cable. However, there are many other antennas which will fulfill this requirement. For a more detailed de scription on antennas , we suggest you refer to the ARRL Antenna Book or The Radio Amateur’s Handbook. -6- Antenna connection to the R-4A is provided at the jack on the rear of the chassis marked ANT. It is recommended that when the R-4A is used with a transmitter, the transmitting antenna be used; change-over being accomplished by an antenna relay. This function is provided internally in our model T-4 and T-4X Transmitters. E. SPEAKER REQUIREMENTS A good quality 4 ohm speaker should be connected to the jack on the rear of the chassis marked SPKR. If one lead of the speaker is grounded to its cabinet, its connection should be to the chassis of the R-4A. Our accessory speaker model MS-4 provides the correct match, correct tonality for good communications audio, correct connector, and is c o m patible in appearance with the R-4A. It will also house our model AC-4 power supply which is needed in conjunction with our model T-4 and T-4X Transmitters. F. ANTI -VOX A high impedance output is provided at the ANTI-VOX jack on the rear of the R-4A chassis for use with our T-4 and T-4X transmitters and other transmitters having voice control capabilities. The impedance at this terminal is approximately 5000 ohms. If the transmitting equipment requires a lower impedance it may be necessary to attach a matching transformer between the ANTI-VOX terminal on the R-4A and the ANTIVOX input terminal of the transmitter, or to use the speaker output. G. MUTING The Mute jack on the rear of the R-4A is connected so that when the function switch is in EXT-MUTE position the receiver will operate only when the inner-conductor of this jack is shorted to ground, and the R-4A will mute when the inner-conductor is open with respect to ground. The inner-conductor should, therefore, be connected to a relay contact in the transmitter or antenna relay which is normally open when transmitting and grounded when receiving. It is recommended that a shielded wire be used between the mute terminal and the relay such as is provided with our model T-4 and T-4X Transmitters. If external muting is not desired, the STBY and ON positions of the function switch can be used. It is necessary to insert a shorted plug in the Mute Jack to obtain N. B. and CAL functions. Such a plug is installed in each R-4A when shipped. -7- TR-4 R-4A AC-4/MS-4 o r R V - 4 y--- -- - ---I I This switch must b e in the TCVR position for transceiving and in t h e RCVR position for separate receiver use. lower C a b l e ~___.____ ~__Speaker Cable -Mute _~--- Line Receiver Antenna J Cable ____--_-_____.p FIG. 1 USING THE R-4A WITH THE TR-4 TRANSCEIVER VIEWING ANGLE OPTIONS REAR FE ET REMOVED INVERTED FRONT FEET OPTION # 2 FEET REMOVED FROM REAR OF BASE ~__ _ _ _ _ STUD* 10x24 x 5 / 8 L O N G SUPPLIED WITH UNIT FIGURE 2 -8- III CONTROL FUNCTIONS A. FRONT 1. MAIN TUNING - The MAIN TUNING knob of the R-4A determines the frequency on which you are receiving. The vernier skirt around this knob is calibrated in KC’s from 0 to 25. The main dial is calibrated in five KC divisions and has two scale S . Use the 0 to .500 scale for bands 7.000-7.500, 14.000-14.500, 21.000-21.500, etc.; use the .500 to 1.000 scale for bands 1.500-2.000, 3.500-4.000, 28.50029.000, etc. The small red knob just to the right of the dial scale is for adjusting the position of the indicator line for calibrating the main dial. The knob skirt is also adjustable by pushing it in slightly and rotating it in the desired direction while holding the main tuning knob stationary. 2. BAND - The BAND control is a six position switch used to select the amateur band desired or to switch the RF circuits to the correct tuning range when tuning accessory frequency ranges. The frequency range which may be tuned for each setting of the band switch control is given on the chart on page 16. 3. XTAL - The XTAL switch is an eleven position switch used to determine which crystal socket will be inserted in the circuit. When it is in the normal position, crystal selection is accomplished by means of the band switch (with the exception of the 1.5 setting). When this switch is set on any of the other positions 1 through 10, the crystal inserted in the corresponding crystal socket will be inserted in the circuit for accessory band operation. The BAND switch must then be set in accordance with the information given on the crystal frequency chart for reception of the frequency desired. 4. PRESELECTOR - The PRESELECTOR control permeability-tunes the antenna, RF, and premixer coupling coils to the desired frequency. The logging scale on this control is calibrated from 0 to 10 with markings showing the correct settings for the 160 through 10 meter amateur bands. 5. FUNCTION - The FUNCTION switch is a six position switch used to select the method of operating the R-4A. When in the OFF position the power transformer primary is opened, thus turning the unit off. When in the STBY position, the power is connected, thus allowing the filament and B+ to operate but the receiver is muted regardless of external connection. When in the ON position, the receiver is unmuted regardless of external muting connection. When in the EXT-MUTE POSITION, the receiver is muted or unmuted depending upon whether or not the mute connection on the rear of the chassis is grounded, thus permitting external control -9- by the transmitter. When in the N. B. position the noise blanker is energized, and when in the CAL position, the noise blanker is switched off and the calibrator is switched on. In these last two positions the muting function is the same as if the switch were in the EXT-MUTE position, so if external muting is not used, a shorted plug must be inserted in the Mute jack to obtain these functions. 6. SSB/CW-AM - This switch determines the detector which is used and the AVC mode. When in the AM position, a diode detector is incorporated, the BFO is switched off, and the AVC with a slow time constant is used. The other three positions under the heading SSB/CW employ a product detector with the BFO. In the SLOW AVC position the AVC delay time is about .7 5 seconds. In the FAST AVC position it is approximately .025 seconds. In the AVC OFF position no AVC is generated. The SLOW AVC position should normally be used with single sideband and CW and the fast position should normally be used for break-in CW and RTTY. The AVC OFF position should be used only on CW under difficult conditions in conjunction with the RF gain control. 7. AF GAIN - The A. F. GAIN knob controls the audio output level of the receiver. 8. RF GAIN - The R.F. GAIN knob varies the bias applied to the AVC controlled tubes thus controlling the R. F. gain of the unit. 9. NOTCH - The NOTCH control tunes a highly selective notch across the receiver’s passband for the purpose of eliminating interfering carriers . When turned to the OFF position, the Notch is moved outside the receiver’ s pa ssband. Rotation of this control is in the same direction from the center as PASSBAND control; i. e. If PASSBAND is set to the left side (lower sideband) then heterodynes will be removed with NOTCH set left of center. 10 ?) PASSBAND - The PASSBAND control is composed of two parts; the passband selector lever and the passband tuning knob. The selector lever is calibrated in numbers representing the band widths in KC’s at 6 DB down(.4, 1 . 2 , 2 . 4 , and 4.8KC). The length and position of the lines which make up the passband tuning calibration indicate the relative band widths and their positions with respect to each other. The pointer on the Passband tuning knob represents the relative position of the fixed 50 KC BFO with respect to the movable passbands. The dots at the ends of the lines indicate the correct settings of the PASSBAND tuning knob for single sideband reception. All of the left hand dots are for lower sideband and all of the right hand dots are for upper sideband. -lO- For CW reception on the . 4 position the signal is tuned for most pleasing note with the frequency knob and is then peaked with the PASSBAND tuning knob. You can then tune other stations without changing the PASSBAND tuning knob setting. The audio frequency at maximum signal strength will be correct. B. 11. PHONE JACK - A PHONE JACK is provided on the front of the R-4A for private listening when desired. The jack automatically mutes the speaker output when headphones are plugged in. While the headphone impedance is not critical (adequate output is available for most commercially available phones) more output is obtained on lower impedance phones . We recommend a good set of 600 ohm phones, such as the Trimm type 56 - 06. 12. S - M E T E R - The S-METER indicates relative signal strength of the received signal. It is calibrated in S-units from S-l to S-9 and DB over S-9. Each S-unit equals about 5 DB and S-9 is about 30 microvolts at the ANT terminal. REAR CONTROLS & JACKS 1. INJ. JACK - The INJ. jack provides a means of coupling the premixer system of the R-4A to the T4 or T4X transmitters so that transceive operation with these units can be obtained. 2. SPEAKER JACK - The SPEAKER JACK on the rear of the chassis is for the connection of a 4 ohm speaker such as our MS-4. 3. MUTE JACK - The MUTE JACK is for externally muting and unmuting the r e c e i v e r . The receiver is muted when the FUNCTION switch is in the EXT-MUTE, N. B., and CAL positions and when the center conductor of this jack is open from ground. Shorting the center conductor to ground returns the receiver to the receive condition. 4. ANTI-VOX JACK - High impedance audio is brought out the ANTI-VOX JACK for use in energizing the ANTI-VOX circuit of a transmitter used with the unit such as our T-4 and T-4X. 5. ANTENNA JACK - The ANTENNA JACK provides a means for connecting the R-4A to an antenna. The input impedance at this point is approximately 52 ohms and can be used with antennas having impedances between 50 and 75 ohms. 6. POWER SOCKET - A POWER SOCKET is provided on the rear of the R-4A for operating external accessories. This plug mates with a Cinch Type 5AB2 connector. Maximum load is 6.3 VAC @ .75 amp and +150 VDC @ 30 ma. -11- C. SIDE CONTROLS & JACKS 1. S-METER ZERO - This control is the front-most adjustment on the right side of the R-4A chassis and is for the purpose of setting the S-meter needle to S-l under no signal conditions. 2. NOTCH ADJ. - The NOTCH ADJ. control located on the right side of the chassis is a balancing device whichdetermines the amount of attenuation obtained with the T-notch filter. This control needs to be set very rarely. For the proper adjustment, see operating instructions . 3. XTAL/VFO SWITCH - This switch, located on the left side of the chassis, allows the operator to select between normal VFO operation or crystal control, using a crystal plugged into the CRYSTAL LOCK SOCKET. 4. CRYSTAL LOCK SOCKET - The R-4A may be crystal locked to a specific frequency by installing a crystal of the required frequency in this socket and setting the XTAL/VFO SWITCH to the XTAL position. For details. see “Fixed Frequency Operation” in the operation instructions. THIS SWITCH MUST BE IN THE VFO POSITION FOR NORMAL OPERATION. Figure #3 REAR VIEW -12- IV OPERATION A. Preliminary Control Settinqs For all modes of operation set these controls as follows: FUNCTION BAND XTALS PRESELECTOR NOTCH R.F. Gain A.F. Gain B. - - On - - Set to desired amateur band (see “accessory frequency coverage” for information concerning coverage of other frequencies) - - NORM - - Peaked for maximum S meter reading on operating frequency - - Off - - Fully clockwise - - Comfortable level Single Sideband or Double Sideband Suppressed Carrier Reception 1. 2. 3. Set the Passband selector lever to 2.4 KC and set the Passband knob to the dot at the end of the third line from the top corresponding to the sideband desired. Set the SSB/CW-AM switch to Slow AVC. Tune in a station with the main tuning for pleasing audio characteristics. If noise is a problem, switch the Function switch to N. B. (see function switch and noise limiter explanation). If interference from undesired stations is a problem, adjust the PASSBAND selector lever to the 1.2 KC position and readjust the PASSBAND knob to the dot at the second line from the top corresponding to the desired sideband. A heterodyne from a nearby carrier can be eliminated with the Notch control. A more detailed description of the use of this control follows under “Operation of Notch Control. C . C . W. Reception 1. 2. 3. Set the Passband selector lever to 1.2 KC and set the Passband knob to either of the dots at the ends of the second line from the top. Set the SSB/CW-AM switch to Slow AVC. Tune in a station for pleasing audio pitch with the main tuning knob and readjust the Passband knob for maximum S-meter reading. -13- Under crowded band conditions it will be advantageous to use the . 4 KC selectivity position and reposition the Passband knob for maximum S-Meter reading on a signal tuned in to the desired pitch. After the Passband control is adjusted thus, simply tune in a C W signal for maximum S-Meter reading and it will automatically be the correct pitch. It will sometimes be to your advantage to shift the passband of the receiver to the other side of the BFO frequency for better copy under crowded band conditions. This can be accomplished simply by repositioning the Passband knob to the alternate dot and retuning the station with the main tuning knob. Noise and strong interfering signals can be attenuated using the N .B. and Notch functions as described later in this section. Many operators prefer no AVC on CW. If this is your preference, turn the SSB/CW-AM switch to the AVC OFF position, turn the A.F. -Gain - - fully clockwise and regulate receiver gain with the R, F. Gain control. D. AM Reception 1. 2. 3. Set the Passband selector lever to 4.8 KC and set the Passband tuning knob to the middle of the longest line. Set the SSB/CW-AM switch to AM. Tune in a signal with the main tuning knob. Interfering heterodynes can now be eliminated using the Notch control, and noise can be reduced or eliminated by turning the Function switch to N. B. A detailed description of these functions follows. E. RTTY Reception 1. 2. 3. Set the Passband selector lever to the 1.2 KC position and set the Passband knob to the right of the dot corresponding to lower sideband. Set the SSB/CW-AM switch to Fast AVC. Tune in a signal with the main tuning knob for correct indication on your terminal unit tuning indicator and adjust Passband tuning knob for equal S-Meter reading of both mark and space. If the station you are copying is sending upside down (mark low-space high) turn the pa ssband control to the left of the “upper” dot and retune the station with the main tuning dial. If noise is a problem, turn the Function switch to N. B. Interfering heterodynes can be eliminated using the Notch control. -14-- F. Adjustinq Dial Calibration The calibration of the main tuning dial on the R-4A may vary slightly from band to band due to the tolerance limits of the various crystals. Therefore, the main tuning dial index has been made adjustable by means of the small red knob to its right. To set the calibration on a given band, proceed as follows: 1. 2. 3. 4. 5. 6. G. Set Band Switch, Preselector, and Xtal switch to the desired band. Set Function switch to CAL. Set SSB/CW-AM switch to Slow AVC. Tune in 100 KC crystal calibrator signal for zero beat at the 100 KC point nearest the desired operating frequency. Slide the red knob at the right of the dial scale until the index line coincides with the 100 KC dial calibration. While holding the main tuning knob, push in on its calibrated skirt and turn until the “0” mark coincides with the indicator line. Noise Blanker Operation The noise blanker in the R-4A is an I. F. device which turns off the receiver during a noise pulse. It is equally effective on all modes of operation and greatly attenuates most impulse noise. For normal operation under ” no noise” conditions, the Function switch should be positioned in other than the N. B. settinq. However, if noise becomes a problem, simply switch to N.B. It will be noticed that the noise blanker functions only when needed: that is when the noise is greater than the desired signal. Due to the effect of AVC in giving constant AF output, the noise may not appear to decrea se. However, signals down in the noise will come up and can be copied which were undetectable previously. It will also be noted that the N.B. works best on noise pulses which are very short in duration and which are separated widely in time, (i.e. automobile ignition noise ) . The closer the pulses are together, the less effective the N. B. will be since the noise detector circuitry has more and more difficulty distinguishing the noise from the desired signal. -15- H. Operation of NOTCH control The notch control on the R-4A consists of a permeability-tuned T-notch filter in the 50 KC I. F. This filter is capable of producing a deep notch which can be tuned across the receiver’s I. F. for the elimination of interfering carriers in all modes of operation. In order to obtain optimum results using this control, it is first necessary to set the “notch adjust” control located on the side of the chassis as de scribed here. 1. Preset R-4A controls as follows: FUNCTION PASSBAND BAND XTALS R.F. GAIN A.F. GAIN SSB/CW-AM NOTCH 2. 3. 4. 5. --------- Cal Selector 2.4 or 4.8, Knob upper or lower 3 . 5 MC NORM Fully clockwise Comfortable level Fast AVC Off With the main tuning knob, tune in the crystal calibrator for low pitched audio note and peak the preselector for maximum S-Meter reading. Advance the Notch control until some reduction in S-meter reading is observed. Adjust Notch Adjust (located on right side of chassis) for further attenuation. Alternately adjust Notch and Notch Adjust for minimum S-meter reading. This is the optimum setting for notching and further adjustment should rarely be necessary. In order to eliminate an unwanted carrier on any mode of operation, tune the Notch control across the Passband of the receiver until the carrier drops into the notch and is thus eliminated. Note that it is just as easy to notch out the desired carrier so a little practice will be necessary to enable the operator to use the control most effectively. Rotation of the Notch control is in the same direction from center as Pa ssband control. That is, if Passband is set to the left side (lower sideband) then heterodynes will be removed with the Notch control set to left of center. -16- I. Accessory Frequency Coverage In addition to reception on 80, 40, 20, 15, and the 28.5 - 29.0 portion of 10 meters, the R-4A can be programed to receive any ten 500 KC-wide ranges between 1.5 and 30.0 mc (excluding 5.0 to 6 .O mc) by inserting the appropriate crystal in one of the ten accessory crystal sockets. These sockets face out the rear of the unit on the left side of the chassis. In order to determine the correct crystal frequency, simply add 11.1 to the lowest frequency of the 500 KC range to be covered. For example; assume you wanted to receive 1.5 to 2.0 MC for reception of the 160 meter amateur band. The crystal frequency would be the lowest frequency of the desired range (1.5 MC ) plus 11.1 which would equal 12.6 M C . This crystal can then be inserted in any one of the ten accessory crystal sockets provided. IMPORTANT: Only series resonant crystals should be used. Accessory crystals may be ordered direct from the R.L. DRAKE COMPANY for $5.00 each. When ordering, be sure to specify that the crystals you desire are for accessory frequency operation in the R-4A. ’ ) In order for the desired band to be received,the X T A L Switch must be turnea to the number corresponding to the crystal socket in which the crystal in question is inserted. The lowest frequency of the range made available may then be written in the range window with pencil for future reference. If crystals are changed you may erase the previously inscribed numbers easily. The BAND switch must now be turned to a position which will allow the PRESELECTOR to tune the desired range. Recommended ranges are as follows: BAND 1.5-3.0 3.5 7.0 14.0 21.0 28.5 PRESELECTOR TUNING RANGE (MC) 1.5 - 3 . 0 3.0 - 5 . 0 6.0 -10.0 10.0 -16.0 16.0 - 2 3 . 0 23.0 - 3 0 . 0 In our example, the BAND switch should be placed in the 1.5 position and the preselector should be peaked on the 160 meter portion of its scale. A chart showing the preselector frequency vs. log scale setting for each Band switch position is shown on page 19. -17- T h e f o l l o w ing table shows the correct crystal frequency, and Band s e t t i n g f o r r a n g e s b e t w e e n 1 . 5 a n d 3 0 m c ( e x c l u d i n g 5 .0 - 6.0 mc) NOTE that if you intend to transceive with the R-4A, the crystal chart in the T4/T4X b o o k s h o u l d b e f o l l o w e d i n s t e a d . When receiving ranges starting with an even megacycle, the 0.000 to . 500 range on the main tuning dial may be used and when receiving ranges starting with a half megacycle, use the ,500 to 1.000 mc scale. Figure #4 CRYSTAL FREQUENCY CHART FREQ. RANGE CRYSTAL 1 . 5 - 2.0 2.0 - 2 . 5 2.5 - 3.0 3.0 - 3 . 5 3.5 - 4 . 0 4.0 - 4.5 4.5 - 5.0 6.0 - 6.5 6.5 - 7.0 7.0 - 7.5 7.5 - 8.0 8.0 - 8 . 5 8.5 - 9.0 9.0 - 9 . 5 9 . 5 - 10.0 10.0 - 10.5 1 0 . 5 - 11 .o 11.0 - 11.5 1 1 . 5 - 12.0 1 2 . 0 - 12.5 1 2 . 5 - 13.0 1 3 . 0 - 13.5 1 3 . 5 - 14.0 14.0 - 14.5 1 4 . 5 - 15.0 15.0 - 15.5 1 5 . 5 - 16.0 1 6 . 0 - 16.5 12.6 13.1 13.6 14.1 14.6* 15.1 15.6 17.1 17.6 18. l* 18.6 19.1 19.6 20.1 20.6 21.1 2 1.6 22.1 22.6 23.1 23.6 24.1 24.6 2 5 . 1 *+ 25.6 + 26.1 + 26.6 + 27.1 BAN D FREQ. RANGE 1.5 - 3.0 1.5 - 3.0 1.5 - 3.0 3.5 3.5 3.5 3.5 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 21.0 CRYSTAL 27.6 16.5 - 17.0 17.0 - 17.5 28. 1 28.6 17.5 - 18.0 29.1 18.0 - 18.5 18.5 - 19.0 29.6 19.0 - 19.5 30.1 19.5 - 20.0 30.6 20.0 - 20.5 31. 1 20.5 - 21.0 3 1.6 21.0 - 21.5 32. l* 32.6 21.5 - 22.0 22.0 - 22.5 33.1 22.5 - 23.0 33.6 34.1 23.0 - 23.5 23.5 - 24.0 34.6 24.0 - 24.5 35.1 24.5 - 25.0 35.6 36. 1 25.0 - 25.5 36.6 25.5 - 26.0 26.0 - 26.5 37.1 26.5 - 27.0 37.6 27.0 - 27.5 38. 1 27.5 - 28.0 38.6 28.0 - 28.5 39.1 28.5 - 29.0 39.6* 29.0 - 29.5 40.1 29.5 - 30.0 40.6 * Supplied with receiver BAND 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 2 1.0 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 + The se ranges not recommended for 6 meter convertors. -18- J. Fixed Frequency Operation The R-4A can be locked to a specific frequency by plugging the appropriate crystal in the crystal lock socket, located on the left side of the chassis, and positioning the XTAL/VFO switch to the XTAL position. When the switch is so positioned, the R-4A VFO and crystal oscillator system will no longer control the frequency. Crystals for this application should be of the parallel resonant fundamental variety with HC-6/U holders. The frequency of the crystal to be used in this socket should be equal to the desired operating frequency +5645 KC or to l/2 of this value if it exceeds 15mc. EXAMPLES: Desired operating freq. 7155KC + 5645 KC = 12.800KC (crystal frequency) or Desired operating freq. 21,145KC + 5645KC = 26,790KC /2 = 13,395KC (crystal frequency) A trimmer capacitor is provided directly below the crystal socket for ” pulling” the crystal slightly in order to get exactly on the desired frequency. The PRESELECTOR and BAND switch should be positioned as described under “Accessory Frequency Coverage” for the desired frequency. If a T4X is being used, placing the T4X TRANSCEIVE switch on SEP.CONT. will result in the T4X being VFO controlled while the R-4A is xtal locked. Placing this switch in the RCVR position will lock the T4X on the R-4A lock frequency. If the switch is placed on XMIT, the T4X controls both receive and transmit frequencies. The lock crystal in the R-4A will then have no effect. Crystals for fixed frequency R-4A operation may be ordered direct from the R. L. Drake Company. When ordering, be sure to specify that the crystal you are ordering is for fixed frequency operation with the R-4A. -2o- V THEORY OF OPERATION A. R.F. Amplifier A signal entering the antenna is applied to the grid of the low noise 12BZ6 R. F. amplifier tube (Vl) through the tuned circuit formed by the coil Tl and capacitors C21 through C31. Here it is amplified and the output is tuned by the circuit formed by coil T2 and capacitors Cl through C11. The signal is then applied to the grid of the 6HS6 first mixer (V2). B. First Mixer and Premixer System A signal from the premixer system is applied to the cathode of the 6HS6 first mixer tube (V2), 5645 KC above the incoming signal frequency applied to its control grid. This results in 5645 KC I.F. output. The premixer system consists of a 4955KC to 5455KC solid state permeability tuned VFO T13, a switchable overtone crystal oscillator Ql, the premixer V8, and the premixer output circuitry composed of T3 and T4 and their tuning and coupling capacitors. The VFO signal is applied to the cathode of the premixer V8 and the output of the crystal oscillator Ql, is applied to the grid. The crystal frequencies are selected so that the difference frequency output of the premixer is 5645 KC above the frequency of the desired incoming signal. For example, on 80 meters a 14.6 mc crystal is used in the crystal oscillator. This frequency and the 4955 - 5455 KC VFO output combine in the premixer stage to give output from 9145 KC to 9645 KC. This signal is applied to the first mixer cathode through coils T3 and T4 and their associated tuning and coupling capacitors to beat with the incoming 3.5-4.0 MC signal. This results in 5645 KC output. Note that the RF coils Tl and T2 and premixer output coils T3 and T4 are premeability tuned, and are ganged together. They are tuned by means of the PRESELECTOR control. -21- c. Second Converter The 5645 KC output of V2 is applied to the grid of the 12BE6 second converter (V3) through a crystal filter. This gives excellent cross modulation and overload characteristics by providing selectivity before the gain producing stages. The cathode, control grid and screen grid are connected in a Pierce oscillator configuration controlled by a 5595 KC crystal. The 5645 KC IF signal is applied to the signal grid of this tube where it beats with the crystal oscillator signal to produce 50 KC output. D. 50 KC I.F. System The 50 KC output of the second converter V3 is applied to the grid of the 12BA6 IF amplifier tube V4 through the T-Notch Filter composed of T8 and its associated circuitry. Output of V4 is applied to the grid of the last 12BA6 IF amplifier ( V - 5 ) through the passband tuner T9. The passband tuner consists of four LC circuits with high Q. Passband tuning is accomplished by ganged permeability tuning of the four coils, and variable selectivity is accomplished by changing the coupling between the four tuned circuits. E. DETECTOR SYSTEMS The amplified signal from V5 is applied to the AM detector composed of diode D7 and Q5, to the AVC amplifier Q4 and to the product detector diodes through the IF transformer, Tl0. When the SSB/CW-AM switch is in the SSB/CW position, the BFO, Q6, is turned on applying 50 KC voltage to the product detector diodes, and beats with the IF signal to produce an audio signal across the AF GAIN potentiometer. When the SSB/CW-AM switch is in the AM position, the BFO is turned off, the AM detector is turned on and its output is connected to the AF GAIN potentiometer. -22- FREQUENCY -8 KILOCYCLES -4 -6 BFO 0 -2 4 2 6 NOTE‘ PASSBANDS ARE CONTINUOUSLY MOVABLE ABOVE 20 AND BELOW EIFO, FREQUENCY. 30 cn ii 3 W 0 40 50 60 FIGURE X 6 - SELECTIVITY CURVES KILOCYCLES -2 -I (6 FO) 0 I 2 3 4 5 6 \ \ \ 6 0 FIGURE # 7-EFFECT OF NOTCH ON 2.4 KC SELECTIVITY CURVE -23- 8 IO F, Audio Output Audio signal from the AF GAIN potentiometer is applied to the grid of the 6EH5 audio output tube V-7 through two stages of AF amplifiers consisting of Q7 and Q8 and associated circuits. The audio output from this tube is then applied to the speaker or phones through audio output transformer T16. The ANTI-VOX jack is connected directly to the plate of V7 through C122. G AVC System The 2N3394 AVC amplifier(Q-4) is biased past cut-off to provide AVC delay. When sufficient R. F. voltage from V5 is applied to its base, collector current flows during part of the cycle. This causes amplified negative voltage to appear across its load resistor R83 thus charging Cl08 when the SSB/CW-AM switch is in the fast AVC position and both Cl08 and Cl09 when the switch is in the slow AVC position. The capacitor or capacitors then discharge through R83 to provide a time constant of about .75 seconds on slow AVC and about .025 seconds on fa st AVC . When the switch is in the AVC off position the load resistor R83 is shorted, thus preventing AVC voltage from being developed. AVC voltage is applied to the grid of Vl, V4, V5, and Noise Blanker IF amplifier V9. Rotating the RF Gain control counter clockwise applies increasingly more negative bias to the AVC controlled tubes thus limiting their gain. Adjustment of the receiver sensitivity control (R87) varies the minimum bias on the AVC controlled tubes under no signal conditions with RF Gain control at maximum. When the mute line is opened from ground, the bias voltage rises to -28 volts, thus cutting off the AVC controlled tubes. H. S-Meter The S-Meter operates in a bridge circuit with the plates of V-4 and V-5 on one leg and V2 and V3 on the other leg, When AVC voltage is applied to the grids of V-4 and V-5, the tubes draw less current, thus unbalancing the bridge and causing the S-Meter to read up scale, Adjustment of S-Meter zero pot (R42) allows the bridge balance to be varied for zeroing the meter. Zero adjustment holds under varying line voltage conditions due to current characteristics of V-2 and V-3. -24- The S-Meter sensitivity control R-40 varies the sensitivity of the meter for calibration purposes by varying the resistance in series with it. I. Noise Blanker The noise blanker in the R-4A attenuates a received noise pulse by shunting to ground the output of V-4 during the time interval of the pulse. In other words, the receiver is turned off during the pulse. The 50 KC I. F. output of the second converter V3 is fed into the grid of the 12BA6 Noise Blanker IF amplifier V9. Here it is amplified to a level sufficient to operate the pulse detector and separation circuit composed of Dl and D2 and their associated circuitry. This circuit operates in such a way that when a noise pulse is received of a level higher than the received signal, a negative pulse is presented to the grid of the noise shaper Vl0A. This stage is normally conducting and a negative pulse causes a large positive pulse to appear at the plate. This pulse is applied to the grid of the pulse amplifier Vl0B. The 18 K resistor R66 and the 100 K resistor R65 form a voltage divider which applies positive cathode bias to Vl0B and diode D3 preventing both from conducting. When a positive pulse is applied to the grid of Vl0B, the bias is overcome causing both Vl0B and D3 to conduct. When D3 conducts, it shunts to ground the output of V4 through Cl04 and C105. J. Crystal Calibrator The cathode, grid #l, and grid #2, of the 12BA6 crystal calibrator (V12) are connected in a Pierce oscillator circuit which operates at 100 KC. The operating point of the plate of this tube is such that it is quite rich in harmonics. This harmonic output is coupled to the antenna jack through capacitor C118. The cathode is disconnected from ground in all but the CAL position of the FUNCTION switch, thus disabling the stage. K. Power Supply The full wave power supply uses two IN3194 diodes. Condenser input is used with +140 and +160 volts output. -25- The negative bias supply uses a IN3194 diode to provide -60 volts to the AVC system for minimum bias, muting, and control of RF Gain. An OB2 voltage regulator VII is incorporated to provide 108 volts regulated for operation of the xtal calibrator. A IN714 zener diode, in conjunction with V11 provides 10 volts regulated for the VFO and H .F. oscillator. The power transformer has a dual primary. As supplied, it is connected in parallel for 120 volt operation. To operate at 240 volts, it will be necessary to remove the GRN/BLACK and YEL/BLACK wires from their present terminals and connect them together at the remaining terminal of the terminal strip. This places the windings in series. It will also be necessary to remove the.75 amp fuse and replace it with a . 4 amp slo-blo fuse. m r Figure #8 -26- -- VI SERVICE DATA We will check and factory align your R-4A for a nominal fee of $10 .OO plus transportation charges if the set has not been tampered with. If repairs are necessary, an additional charge will be made. Units that have been tampered with or misaligned, will be repaired on a time and material basis only. A. Removinq Top Cover 1. 2. B. Removinq Bottom Cover 1. 2. c. Remove the three top screws on each side of the R-4A. Remove cover by first pulling up on the rear and then on the front of the cabinet. Remove the six bottom screws from the sides of the R-4A Lift R-4A chassis out of bottom cover. Tube Replacement In general, most trouble encountered in radio equipment of good design is due to tube failure. The R-4A has been designed so that tube replacement can be done without need for realignment. The best method of finding defective tubes is direct substitution. It is best not to rely too heavily on a tube checker. D. Troubleshooting Careful consideration has been given in the design of the R-4A to keep maintenance problems to a minimum. However, it is quite possible that some problem will arise which cannot be cured by tube substitution. If this occurs, we suggest that you either return the unit to your dealer, or write direct to our Service Department, describing your problem in detail. Include full information concerning external connections, control settings, tubes substituted, etc. DO NOT RETURN EQUIPMENT TO THE FACTORY WITHOUT PRIOR AUTHORIZATION. The voltage and resistance charts which follow should be valuable in isolating minor problems. However, no attempt should be made to service the R-4A unless you are thoroughly familiar with electronic circuitry and servicing technique. CARE SHOULD BE TAKEN NOT TO DISTURB THE LEAD DRESS IN THE R-4A SINCE SEVERAL CIRCUITS ARE QUITE CRITICAL IN THIS REGARD! -27- Figure #9 VOLTAGE CHART Number Type 1 2 3 4 5 6 7 Vl 12BZ6 -1.1 1.66 0 12.6* 140 129 0 v2 6HS6 0 0 6.3* 12.6* 140 80 2.8 v3 12BE6 -11.5 2.7 12.6* 0 140 132 0 v4 12BA6 -1.1 0 0 12.6* 136 93 2 v5 12BA6 -1.2 0 12.6* 0 110 80 0 v7 6EH5 2.9 0 12.6* 6.3* 0 91 140 V8 6HS6 -.8 0 0 6.3* 145 120 2.2 v9 12BA6 -1.29 0 12.6* 0 128 110 0 Vl0 12AX7A 70 -* 5 0 0 12.6* 148 0 Vll OB2 110 N.C. N.C. N.C. 110 N.C. .7 v12 12BA6 -44 0 0 12.6* 44 45 l7 9 2.7 N.C. Notes: * Indicates AC voltage. Function switch is in NB position except for V12 measurements where CAL position is used. 3. R.F. and A.F. gain controls are fully clockwise. Side controls are set for normal operation. SSB/CW-AM switch is in Slow-AVC position. Band switch is on 3.5 and Preselector is peaked on 80 meter noise with ant. 4. disconnected. Xtal switch is on NORM. 5. The position of other controls is unimportant. However, the shorted mute plug must be inserted in the MUTE jack. 1. 2. -28- Figure #l0 RESISTANCE CHART - Number Type 3 4 5 6 7 8 9 20K* Fil - Vl 12BZ6 4.4M 0 Fil 6K 6.5K 0 v2 6HS6 2.2M Fil Fil 6.5K 228K 2.2K v3 12BE6 Fil 0 6.5K 6.5K 0 v4 12BA6 4.2M 0 Fil 6.5K 9K 330 V5 12BA6 3.7M Fil 0 10K 12K 0 v7 6EH5 100 Fil Fil 500K 16.1K 7.2K V8 6HS6 350K 0 Fil 4.7K 25K 500 v9 12BA6 2.6M Fil 0 6.5K 8.3K 0 VlO 12AX7. A 158K 0 0 Fil 4.5K 3.2M Vll OB2 5K 700K INF 700K 5K INF 9* v12 12BA6 1M 0 0 Fil 390K 125K 1K 500K Note s: 1. * This resistance will vary greatly on various Ohm meter ranges due to the characteristics of diode D3. 2. Function switch is in NB position for all but V12 where CAL position is used. 3. SSB/CW-AM switch is on slow-AVC, and AF and RF Gain controls are fully clockwise. 4. All side controls are in their normal operating positions. 5. The position of other controls is unimportant. However, the shorted mute plug must be inserted in the MUTE jack, -29- VII ALIGNMENT INSTRUCTIONS Alignment of the R-4A will require the following equipment. 1. A reasonably stable signal generator having a frequency range from 1.5 to 30.0 mc and variable output level. An 11 megohm vacuum tube volt meter (VTVM) 2. A 12.6 mc series resonant crystal. A WWV crystal for the WWV frequency most reliable in your area ( see ” accessory frequency coverage”) An alignment load consisting of a .005 mfd disk ceramic capacitor in series with a 1000 ohm l/2 watt composition resistor. Small alligator clips connected to each end would be a great help. Two 10K l/2 watt resistors and one 68 ohm resistor. An accurate rule with l/32” divisions. 3. 4. 5. 6. 7. Before alignment is attempted, the R-4 should be turned on and allowed to operate for at least one half hour. A. 50 KC Oscillator Aliqnment 1. 2. 3. 4. 5. 6. B. Set the SSB/CW-AM switch to fast AVC. Set Function switch to CAL. Connect a 6” lead to your alignment load and connect it from pin 5 of the 12BA6 (V5) to pin 5 of the crystal calibrator (V12). Advance A.F. gain control so that an audio beat note can easily be heard. Adjust Tll for zero beat. Note: Do not be concerned that 100 KC calibrator has not yet been set. It cannot be “pulled” far enough off frequency to be of any consequence for this purpose. Remove alignment load. 50 KC I. F. Aliqnment 1. 2. 3. 4. 5. 6. Set the Passband selector lever to 4.8 KC and set the Passband tuning knob to the middle of the longest line. Attach the signal generator to pin 7 of V3 and adjust the frequency to approximately 5645 KC. As 5645 KC is approached you should hear a loud beat note in the speaker. The generator frequency should be adjusted for zero beat. Adjust the generator output for an S meter reading of approximately s-9. Adjust T7 and Tl0 for maximum S meter reading. Note that tuning of these cans will be quite broad. Attach a VTVM to TP-1. Adjust T14 for maximum positive voltage on VTVM (Do not remove VTVM from TP- 1 yet) . C. Crystal Filter and Filter Match Transformer Aliqnment 1. 2. 3. 4. 5. 6. 7. 8. 9. D. Attach signal generator to pin #l of V2 and set generator frequency to 5645 KC. Set level so that an S-Meter reading of approximately S-9 is obtained. Set Passband selector switch to 2.4 KC and set Passband knob until it points horizontally to the left. Adjust signal generator frequency for peak S-Meter reading. A high pitched audio tone should be audible from the speaker. Adjust generator frequency so that the tone increases in pitch. You will notice that the S-Meter reading will start to drop. Continue shifting the generator frequency until the S- Meter reading drops 20 DB. (If the meter reads S-9 at peak, it should now read S-5). Adjust T5 and T6 for maximum S-Meter reading. Return Passband selector lever to 4.8 and return Passband knob to center of longest line. Set generator frequency to image frequency at 5545 KC and adjust generator output level until a signal is heard from the speaker. Note the wires wrapped around pins on the base of the crystal filter can (T6). Unwrap one of these wires until minimum signal strength is obtained. (Note: Unwrapping the wrong wire will result in an increase rather than a decrease in this signal). If much adjustment is necessary here, steps 1 through 6 should be repeated. 5 59 5 KC 0 scilla tor Aliqnment 1. 2. 3. 4. 5. 6. Return Passband selector lever to 4.8 KC and Passband tuning knob to the center of the longest line. With signal generator still attached to pin 1 of V2, and VTVM still attached to TP-1, adjust the generator frequency for maximum positive voltage. This frequency should be very near 5645 KC. Observe this peak voltage and tune the generator in either direction from the point until the voltage drops 50%. Observe the generator frequency reading at this point. Now tune the generator in the opposite direction until the voltage is once again 50% of peak and observe the frequency. Set the generator exactly half way between these two points and adjust C61 for zero beat from the speaker. Disconnect generator and VTVM. NOTE: If R4A is to be used with T4 or T4X, a more accurate adjustment of C61 will be required. See T4/T4X instruction book. -33- E. Antenna, RF, and Injection Circuit Aliqnment 1. Turn off receiver and temporarily connect a 10K resistor from the side rotor contact of S 5 C to ground, and from the corresponding contact of S5D to the nearby terminal strip terminal to which the red and white striped B+ wire is attached. S5C and S5D are the third and fourth bandswitch waffers as viewed from the front of the receiver. You will note that each of these switches have two rotor contacts . The ones in question are the most easily accessible. All rotor contacts are green in color. 2. Disconnect the antenna and connect the 68 ohm resistor across the antenna jack. 3. Install the 12.6 mc crystal in one of the R4 accessory sockets for alignment of the 160 meter band. 4. Turn the PRESELECTOR fully clockwise and carefully measure the distance from the top of the white sleeves protruding from the top of Tl, T2, T3 and T4 to the tops of their respective slugs. This distance should be exactly 9/16”. If necessary, adjust the slugs to this setting. (This was done at the factory and should be correct. Check measurements carefully before altering the position of any of the se slugs .) 5. Turn on receiver and tune in the crystal calibrator signal at 28.5 mc. Set the PRESELECTOR knob so that the slugs are 15/32” above the white sleeves. 6. Adjust all four trimmers marked 28.0 for maximum S-meter reading. (If the S-meter reading is insufficient to produce an adequate S-meter indication, it will be necessary to use the external signal generator. Set the generator output level for an S-meter reading of about S7 and set the generator frequency to 28.5 mc. 7. Repeat steps 5 and 6 for each band using the slug measurements and frequencies given in the following chart. BAND SLUG HEIGHT FREQUENCY 28.5 21 .o 14.0 7.0 3.5 1.5 15/32” 7/1 6” 1 l/3 2” 3/1 6” 0 (flush with sleeve) 0 (flush with sleeve) 28.5 21.3 14.3 7.3 3.8 1.9 mc mc mc mc mc mc NOTE that for the 1.5 BAND adjustment the XTAL switch must be in a position corresponding to the socket in which the 12.6 mc crystal is inserted. This completes the alignment. Turn off the receiver and remove the 10 K and 68 ohm resistors installed in steps 1 and 2. -34- 100 KC Calibrator Alignment F. 1. Attach the antenna to the R-4A and tune in WWV at the frequency most reliable in your area. For crystal selection see the chart on page 18. 2. Set the Function switch to CAL. (A shorted plug must be inserted in the Mute jack). Adjust the calibrator adjust trimmer (C119) for zero beat with the unmodulated WWV carrier. Note that Cl19 is located under the chassis on the component board on which the 100 KC crystal is mounted, and is accessible through a hole if bottom cover is in place. 3. G. V.F.O. Adjustment The permeability tuned VFO was carefully adjusted at the factory and should require no further alignment. If the VFO does not appear to track from one end of the range to the other, it should be returned to our plant for alignment. Maximum calibration error is 1 KC when calibrated at nearest 100 KC point. If you notice the same error from one end of the band to the other and you cannot correct it with the movable dial index, the main dial may be slipped on its shaft enough to bring the calibration back into range. H. Notch Filter Aliqnment 1. Tune in the crystal calibrator signal at any frequency for zero beat. 2. Set the Notch control to the center of its range. 3. Adjust the slug in T8 for minimum S-Meter reading. I. Pas sband Tuner Alignment Turn Passband tuning knob through its rotation and observe the travel of the four slugs visible from the rear of the tuner. 2. When these slugs are nearest the rear of the receiver, the Pass- 1. -35- 3. 4. 5. band tuning knob should be pointing horizontally to the left as viewed from the front. If it is not, loosen the knob set screw and reposition the knob. Tune in a crystal calibrator signal at 3.8 mc for zero beat. Set the Passband selector lever to .4 and set the Passband tuning knob to the center of the shortest line. Attach a VTVM to the AVC test point (TP-2) and adjust the four slugs on the rear of the passband tuner for maximum AVC voltage. The passband tuner slugs have a considerable amount of IMPORTANT spring when turned and this must be taken into consideration when the slugs are adjusted so as to obtain a true peak. 6. 7. 8. 9. 10. 11. J. Set the Passband selector switch to 1.2 KC and turn off the crystal calibrator. Turn the Passband knob through its range while observing the pitch of the received noise. Adjust the small screw on the rear of the tuner until the pitch of the noise is the same at the extreme ends of the control travel. (Pointer pointing horizontally to the left and to the right.) Set the Passband selector lever to the 2.4 KC position and observe the pitch of the noise at the dots at the ends of the second line from the bottom. The pitch should be the same at either dot. If it is not, turn the knob to the left dot and observe the pitch. Then rotate the control to the right until the pitch is the same. Loosen the knob set screw and rotate the knob until it is halfway between its position at step 9 and the right dot. Tighten set screw. Bias and S-Meter Adjustment 1. 2. 3. 4. Attach a VTVM to TP-2 and with the Preselector detuned and the antenna disconnected, adjust the RCVR SENS control, located on a component board directly behind Tll , for - 1.3 5 volts. Remove the VTVM and adjust the S-Meter Zero control, located on the side of the chassis, for a reading of S-l on the S-Meter. Rotate the R.F. Gain control fully counter clockwise and adjust the S-Meter Cal adjustment (R40) located on the component board mounted directly behind V5 for an S-Meter reading of 60DB over S-9. Recheck steps 2 and 3 with the unit sitting upright. Readjust if necessary. -36-